1. Field of the Invention
The present invention relates to a webbing tension device which imparts tension to an occupant restraining webbing to closely restrain an occupant of a vehicle during an emergency situation.
2. Description of the Prior Art
Seatbelt systems for restraining an occupant of a vehicle during an emergency situation are constructed so that the occupant wears an occupant-restraining webbing, one end of which is wound in a webbing retractor.
This webbing retractor for winding the webbing therein imparts predetermined tension to the webbing. However, since the retracting force of the webbing retractor is made relatively small or zero so as not to give the occupant a feeling of oppression, a clearance or slack between the webbing and the occupant wearing the same is often formed. Accordingly, there is concern over the fact that the occupant wearing the webbing may be moved forward in the vehicle by the amount of the clearance or slack in the webbing in an emergency vehicular situation before the occupant is securely restrained by the webbing.
In order to overcome this problem, webbing tension devices have been proposed where a large biasing force from a large spiral spring is transmitted to a webbing takeup shaft of the webbing retractor, so that a substantial tension is imparted to the webbing in an emergency vehicular situation.
In such a webbing tension device, in an ordinary vehicular situation, the webbing is weakly biased in the webbing winding direction by a small spiral spring, but in an emergency vehicular situation, the large biasing force of the large spiral spring is transmitted to the takeup shaft so that the webbing is forcibly wound on the takeup shaft. However, the large biasing force continues to act upon the takeup shaft even after the termination of the emergency vehicular situation, which results in deterioration in the operability of the webbing retractor when the webbing is released from its occupant restraining position or when the seatbelt system is reused.